This invention relates to a method of manufacturing a metal bonded abrasive product, particularly one wherein the abrasive is diamond.
Metal bonded diamond products are used extensively in cutting, milling and drilling. These products consist of a mass of discrete diamond particles dispersed in a metal bonding matrix. The metal bonding matrix will typically be cobalt, tungsten, nickel or iron, alone or containing a relatively low melting alloy such as bronze.
The most commonly used methods for producing such products are the hot press method, the free sinter densification method and the infiltration method.
The hot press method involves mixing the metal powder and diamond and then cold pressing the mixture to a desired shape. The pressures used in this step are typically between 50 and 300 MPa. The shaped product is then packed into a graphite mould pack. This mould pack is placed in a hot-press machine where it is subjected to elevated temperature and pressure. The elevated temperature is typically in the range of 800 to 1100.degree. C. and the elevated pressure is typically in the range of 10 to 50 MPa. A volume change of up to 50% is not uncommon and the final density is usually 92 to 98,5% of theoretical density.
In the free sinter densification method, the manufacture of the cold pressed product is the same as in the hot press method. Thereafter, the shaped cold pressed product is placed on a support and sintered at a temperature of around 1000.degree. C. No pressure is applied nor is a graphite mould pack used. There is thus nothing restraining the product during sintering. A volume change of up to 50% is not uncommon and the final density is usually 92 to 98,5% theoretical density.
The infiltration method involves cold pressing the mixture as for the hot press method. Thereafter, the shaped cold pressed product can be placed on a support with no graphite mould, or a graphite mould can be used. An infiltrant such as a copper based material in strip or granule form is placed on top of the product and this is all typically heated to a temperature of 950-1150.degree. C. This causes the infiltrant to become liquid and to be drawn into the product thus filling the remaining spaces between the powder and diamond in the cold pressed product. There is generally no volume change and the final density is usually 100% of theoretical density.
In the methods described above the final density approaches 100% theoretical density with very little porosity in the final product.
Other methods of producing metal bonded abrasive products include the use of high pressure hot isostatic pressing. This method has the effect of removing porosity from the product, but is expensive. A hot isostatic pressing is often added as a final step to the other methods described above which has the effect of removing the porosity almost completely.
Another known method is to attach a single layer of diamond particles on to the surface of a substrate by means of electroplating.